Scientists say they have been able to make long-lasting blood vessels from human cells.

A US team at Duke University say they overcame what is a major stumbling block - the short life-span of the cells used to make the blood vessels.

In the Lancet, they say they have solved this by infecting the donor cells with a harmless virus carrying an enzyme to encourage longevity.

They say in five years, heart patients may be able to grown their own grafts.

Our work represents a crucial initial step towards growing blood vessels that could be used to treat patients with vascular disease

Lead researcher Dr Laura Niklason

The overwhelming cause of heart disease is atherosclerosis, the build-up of fatty materials within the walls of the arteries.

At the moment doctors have to use other blood vessels, such as those taken from the patient's legs, or artificial grafts to bypass blockages.

However, as these people tend to be elderly, often they do not have any suitable, healthy vessels that can be used for the repair or the vessels have already been used for a previous bypass operation.

Although artificial grafts can work well, when the diameter of the vessels they are replacing are very small, such as those in the heart, they can be prone to complications, such as clotting.

New vessels

So scientists have been looking at ways to make new vessels from scratch using human cells from the patient.

This avoids the potential for rejection, which could occur if cells came from someone else.

Dr Laura Niklason and colleagues took samples of discarded vein from five elderly men after they had undergone conventional coronary artery bypass surgery.

From these they isolated blood vessel cells and infected some of the cells with a virus carrying the enzyme human telomerase reverse-transcriptase (hTERT).

The purpose of this was to increase the life-span of the cells.

All human cells have "inbuilt timers" called telomeres, which shorten every time a cell divides.

Cells from older people have shorter telomeres and therefore can multiply far less than cells from younger people.

Durability

This is a problem if they are to be used to make new vessels because a large number of cells must be grown from a relatively small sample.

There are problems that need to be overcome

Dr Ian Zachary of the British Heart Foundation

By treating the cells with hTERT the researchers were able to engineer more and better quality cells from which to make the blood vessels.

By blocking the telomere timers, hTERT helped the cells to keep on multiplying.

Dr Niklason said: "Our work represents a crucial initial step towards growing blood vessels that could be used to treat patients with vascular disease.

"We have to work out ways to increase the amount of collagen protein made by the vascular cells which will make the blood vessels stronger.

"They are not strong enough yet to function long-term as a vascular graft."

She said they were probably only a couple of years away from remedying this.

Dr Ian Zachary, from the British Heart Foundation laboratories at University College London, said: "This is an exciting initial step.

"Though this approach has a lot of potential, there are problems that need to be overcome before engineered blood vessels can be used to treat patients."

As well as the issue of durability, he said: "There are also potential risks with using cells that have an artificially increased lifespan, the two most important being the risk of tumour formation, and the possibility that the cells in the engineered vessels might proliferate excessively and therefore disrupt the normal structure of the vessel.

"The authors have gone some way to examining these risks, but more work needs to be done."